Narrative:

While on final approach to runway 19R at sna, the pilots were given a traffic advisory of an aircraft on base to runway 19L along with their landing clearance. At about 700' on the radar altimeter the TCAS gave a TA on the TCAS scope (a yellow diamond) and the aural 'traffic, traffic.' the aircraft in question was an small aircraft Y in a turn from base to final for runway 19L. At 400' radar altitude and on localizer and G/south we received a RA of aural 'climb, climb' (and the diamond turned red on the scope). The lights around the vertical speed indicator turned red from 0 to 2000 FPM down and green from 0 to 500 FPM up, indicating we should climb to 0 to 500 FPM to avoid the traffic. We passed the small aircraft Y and continued with a normal landing. Xyz company large transport/widebody transport operating manual section 13 page 33 says: 'no RA's are issued below 500'.' this is the second time now that I have witnessed this is not true. It also states, 'when TCAS issues an RA, the pilot must always maneuver the aircraft per TCAS instructions, even when in visibility contact with a target.' right now bulletin 144, 12/90 does supercede these requirements while in the TCAS test period. 1) I question the performance of TCAS. 2) I feel the PIC should always have the option of compliance with TCAS, particularly in visibility contact. TCAS should be a tool, not a controller. 3) I think the sensitivity of the unit is such that only TA's be issued below 1000' AGL and all alerts be inhibited below 500' AGL. 4) scope clutter makes the unit useful only in the shortest ranges when in a high density area (lax, dfw, ord, etc). In addition, ground traffic on the scope is a problem. 5) I do like the TCAS as a traffic awareness tool. It does need refinement.

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Original NASA ASRS Text

Title: TCAS II ISSUED A RA BELOW 500' AGL.

Narrative: WHILE ON FINAL APCH TO RWY 19R AT SNA, THE PLTS WERE GIVEN A TFC ADVISORY OF AN ACFT ON BASE TO RWY 19L ALONG WITH THEIR LNDG CLRNC. AT ABOUT 700' ON THE RADAR ALTIMETER THE TCAS GAVE A TA ON THE TCAS SCOPE (A YELLOW DIAMOND) AND THE AURAL 'TFC, TFC.' THE ACFT IN QUESTION WAS AN SMA Y IN A TURN FROM BASE TO FINAL FOR RWY 19L. AT 400' RADAR ALT AND ON LOC AND G/S WE RECEIVED A RA OF AURAL 'CLB, CLB' (AND THE DIAMOND TURNED RED ON THE SCOPE). THE LIGHTS AROUND THE VERT SPD INDICATOR TURNED RED FROM 0 TO 2000 FPM DOWN AND GREEN FROM 0 TO 500 FPM UP, INDICATING WE SHOULD CLB TO 0 TO 500 FPM TO AVOID THE TFC. WE PASSED THE SMA Y AND CONTINUED WITH A NORMAL LNDG. XYZ COMPANY LGT/WDB OPERATING MANUAL SECTION 13 PAGE 33 SAYS: 'NO RA'S ARE ISSUED BELOW 500'.' THIS IS THE SECOND TIME NOW THAT I HAVE WITNESSED THIS IS NOT TRUE. IT ALSO STATES, 'WHEN TCAS ISSUES AN RA, THE PLT MUST ALWAYS MANEUVER THE ACFT PER TCAS INSTRUCTIONS, EVEN WHEN IN VIS CONTACT WITH A TARGET.' RIGHT NOW BULLETIN 144, 12/90 DOES SUPERCEDE THESE REQUIREMENTS WHILE IN THE TCAS TEST PERIOD. 1) I QUESTION THE PERFORMANCE OF TCAS. 2) I FEEL THE PIC SHOULD ALWAYS HAVE THE OPTION OF COMPLIANCE WITH TCAS, PARTICULARLY IN VIS CONTACT. TCAS SHOULD BE A TOOL, NOT A CTLR. 3) I THINK THE SENSITIVITY OF THE UNIT IS SUCH THAT ONLY TA'S BE ISSUED BELOW 1000' AGL AND ALL ALERTS BE INHIBITED BELOW 500' AGL. 4) SCOPE CLUTTER MAKES THE UNIT USEFUL ONLY IN THE SHORTEST RANGES WHEN IN A HIGH DENSITY AREA (LAX, DFW, ORD, ETC). IN ADDITION, GND TFC ON THE SCOPE IS A PROB. 5) I DO LIKE THE TCAS AS A TFC AWARENESS TOOL. IT DOES NEED REFINEMENT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.